Magnetic recording apparatuses represented by hard disk drives are expected to provide a largely increased amount of storage in response to the recent advancement of information in society. In order to provide a largely increased amount of storage, it is necessary to increase recording density per unit area of the magnetic recording apparatus. The improvements of the high-sensitive technique of a read element using a magnetoresistive effect and of the track width-narrowing technique have been advanced.
For a low recording density of several Gb/in2, an anisotropic magnetoresistive effect (AMR) is used to convert a magnetic signal on a recording medium into an electric signal. For a high recording density in excess of several Gb/in2, a read element using higher-sensitive giant magnetoresistive effect (GMR) has been used. However, along with the further advancement of high recording density, it is essential to use a high-sensitive read element of a current perpendicular to the plane-type (CPP-type) GMR (CPP-GMR) or of a tunneling magnetoresistive effect (TMR). In addition, to narrow a track width, the development of technology for narrowing the size of resist through exposure conditions has been advanced in mask pattern formation.
The basic structure of a CPP-type magnetoresistive effect head is shown in FIG. 11, which is a cross-sectional view of a read element as from the direction of an air-bearing surface. The CPP-type magnetoresistive effect head includes a magnetoresistive effect film including a free layer 31 and a pinned layer 33 both made of alloy containing a ferromagnetic body, an antiferromagnetic layer 34 adapted to fix the magnetizing direction of the pinned layer 33 and an intermediate layer 32 made of a nonmagnetic material sandwiched between the free layer and the pinned layer; magnetic shield layers 14 and 10 disposed on and below, respectively, the magnetoresistive effect film 11 and serving as electrodes; a refill insulation film 12 adapted to electrically insulate the electrode; and a magnetic domain control layer 13 adapted to control the magnetizing direction of the free layer 31 through the refill insulation film 12.
The free layer 31 varies its magnetizing direction in response to a magnetizing direction input from the magnetization information recorded in a recording medium. When the free layer 31 varies its magnetizing direction, the resistance of a magnetic sensor portion is changed in response to a difference between the magnetizing direction of the free layer and that of the pinned layer. A hard disk drive is configured to convert the change of the resistance into an electric signal and read it. Thus, it is necessary to apply the electric current to read the resistance change of the magnetic sensor portion and the upper and lower magnetic shield layers 14, 10 also serve as electrode films.
The magnetic domain control layer 13 is configured to be disposed as close to the ends of the free layer as possible and to apply a bias magnetic field to the free layer 31. This is because of the following. The magnetizing direction of the free layer 31 is changed in sensitive response to an imperceptible recording magnetic field of information recorded in the recording medium. Application of the bias magnetic field is needed to ensure the reproducibility and stability of the initial magnetizing state and a magnetizing state changed when the recording magnetic field is inputted. Specifically, the free layer 31 which executes magnetization rotation upon receipt of a magnetic field from the magnetic recording medium may have multiple magnetic domains instead of a single magnetic domain structure. In this case, when a recording magnetic field is inputted, magnetic domain wall movement occurs, which causes various noise such as Barkhausen noise. In addition, the reproducibility of the initial magnetization state and the magnetization state at the time of magnetization is lost, which appears as a phenomenon such as output fluctuations. Consequently, the quality of a read signal is deteriorated. To bring the multiple magnetic domains of this free layer into a single magnetic domain structure, a bias magnetic field is applied to the free layer.
The track-width formation process of a CPP-type read element uses a lift-off method as described in Japanese Patent Publication No. 2-17643 (“Patent Document I”). A T-shaped resist pattern is formed on a magnetoresistive effect film formed on a lower electrode. The magnetoresistive effect film is patterned by ion milling using the T-shaped resist pattern as a mask. Thereafter, a refill insulation film and a magnetic domain control layer are formed with the T-shaped resist pattern left, and the T-shaped resist pattern is removed. At this time, a width of a dent called an under-cut at the skirt of the T-shaped resist pattern is controlled, whereby the refill insulation film and the magnetic domain control layer become a discontinuous film. The refill insulation film and the magnetic domain control layer formed on the resist pattern are removed along with the resist-solving process. Thereafter, an upper electrode is formed thereon.
However, in the case of intending to fabricate an element with a track width of less than 100 nm, even if the narrow mask pattern can be formed by advanced exposure technology, it becomes difficult to control the under-cut, which poses a problem in that the lift-off cannot be performed.
Japanese Patent Publication No. 2004-342154 (“Patent Document 2”) describes the fact that the problem with the difficulty of lift-off in which a magnetic domain control layer is removed from above a magnetoresistive device can be prevented by the following. A mask is used to pattern the magnetoresistive element and the magnetic domain control layer is laminated on the mask remaining left. Thereafter, the magnetic domain control layer formed on the mask and a mask surface layer are removed by a planarizing process using chemical mechanical polishing (CMP) to expose the mask. The mask thus exposed is removed. Further, Patent Document 2 describes the fact that the magnetic head can be fabricated in which an upper electrode formed after the removal of a mask is joined to a magnetoresistive effect film through a projecting portion extending therefrom toward the magnetoresistive device.
Japanese Patent Publication No. 2004-186673 (“Patent Document 3”) describes a method of removing a resist pattern by using CMP during lift-off process. According to this method, a first CMP stopper is disposed on the magnetoresistive effect film and a second CMP stopper is disposed on a lead layer including a magnetic bias layer and a conductive layer disposed on both sides of the magnetoresistive effect film. The resist pattern and an unnecessary film on the resist pattern are removed by CMP. In this way, a read element having a narrow track-width can be fabricated.
In the CPP-type magnetoresistive effect head (CPP-GMR head, TMR head), a magnetic domain control layer is disposed on both sides of a sensor junction via an insulating film, so that a distance between a free layer and a magnetic domain control layer is increased. Therefore, a magnetic domain control layer is needed that is thicker than that of the CIP structure which allows detection current to flow parallel to the surface of the magnetoresistive effect film. To meet the necessity, it is necessary to allow a magnetic domain control layer to protrude upward from the upper surface of the magnetoresistive effect film.
The magnetic head described in Patent Document 2 is provided with an upper insulation film between a magnetic domain control layer and an upper magnetic shield so that the film thickness of the magnetic domain control layer cannot be increased.
As described in Patent Document 3, the lift-off using CMP can remove the unnecessary resist of the device track portion and a magnetic domain control layer by the planarizing effect of CMP. However, a problem simultaneously arises in that the magnetic domain control layer not protected by the CMP stopper film is scraped beyond necessity. For example, as shown in FIG. 12, a first CMP stopper film 15 is formed on top of the magnetoresistive effect film 11 and patterning is performed using a resist pattern 18. Then, a refill insulation film 12 and a magnetic domain control layer 13 are laminated on both sides of the magnetoresistive effect film 11 and a resist pattern 18 and on top of the resist pattern 18. A second CMP stopper film 16 is formed on top of the magnetic domain control layer 13 thus laminated. In this state, a step is generated between the first CMP stopper film 15 and the second CMP stopper film 16. However, the CMP process has an effect of planarizing the step. In this state, the lift-off process is performed by CMP. Consequently, a portion of the refill insulation film 12 and magnetic domain control layer 13 which have a large CMP polishing rate and which are not protected by the first CMP stopper 15 and the second CMP stopper 16 as shown in FIG. 13 is scraped off by CMP as shown in FIG. 14. This is because of the following. DLC formed as the stopper film has high-hardness but is a brittle material. If DLC is formed into a thin film, a polishing rate of the thing film is low for CMP in a planar direction but is high at an end portion of the thin film. The magnetic domain control layer 13 cannot be protected and is scraped. As a result, the film thickness of the magnetic domain control layer 13 is reduced in the vicinity of the device, leading to a reduced bias magnetic field. The CPP structure magnetic head needs insulation by refill and thus the distance between the free layer and the magnetic domain control layer is increased. The reduced bias magnetic filed due to the reduced thickness of the magnetic domain layer has a larger influence than the CIP structure head. Thus, during manufacture of the CPP type magnetoresistive effect head, if the lift-off process using CMP is adopted, the magnetic domain control layer is scraped off. This poses a problem in that it is hard to manufacture a read head with high-stability.